Water electrolytic apparatus

ABSTRACT

A water electrolytic apparatus includes, and a plurality of water electrolytic cells each having a solid polymer electrolyte membrane, an anode, and a cathode, the anode and the cathode being arranged on opposite sides of the electrolyte membrane, respectively. The water electrolytic cells are developed on a hypothetical plane and electrically connected in series to one another. In the water electrolytic apparatus, an increase in electric current can be inhibited.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a water electrolytic apparatusused mainly for producing hydrogen.

[0003] 2. Description of the Related Art

[0004] As such an apparatus, a conventional water electrolytic apparatusis disclosed in Japanese Patent Application Laid-open No. 6-33283.

[0005] A general water electrolytic apparatus has an electrode area ofaround hundred square centimeters. If the water electrolytic apparatusis operated at a current density of 1 A/cm², electric current of severalhundred amperes is required, leading to inevitable loss in ohm and theextreme thickening of a cable. The thus-required large electric currentalso leads to a reduction in efficiency of the converter, for example,in the case where a DC/DC converter is mounted at an upstream side of aninput electric power. To produce the same amount of hydrogen avoidingthese problems, it is necessary to decrease the electrode area (if thecurrent density is fixed at 1 A/cm², the area is reduced to ¼, and thecurrent is reduced to ¼), and to increase the number of the waterelectrolytic cells (if the area is reduced to ¼, the number of the waterelectrolytic cells is increased four times produce the same amount ofhydrogen).

[0006] However, if a plurality of water electrolytic cells are laminatedas in the prior art, there is a limit in number of cells laminated. Asthe area of the water electrolytic cell is reduced and the number of thewater electrolytic cells is increased, it is more difficult to maintainuniform performances. When a water electrolytic apparatus having a powersupply is formed by combining a water electrolytic apparatus of alaminated structure, for example, with a panel-shaped solar cell, thefollowing problem is encountered: When the water electrolytic apparatusand the solar cell are superposed one on another from the demand for thecompactness, the height of the entire system is increased and hence, theentire system is not suitable to be placed on a roof or the like.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to providea water electrolytic apparatus of the above-described type, which is ofa thin type, wherein an increase in electric current is inhibited, andeven when it is superposed on a panel-shaped solar cell, the height ofthe entire system can be suppressed to a low level.

[0008] To achieve the above object, according to the present invention,there is provided a water electrolytic apparatus comprising a pluralityof water electrolytic cells each having a solid polymer electrolytemembrane, an anode, and a cathode, the anode and the cathode beingarranged on opposite sides of the electrolyte membrane, respectively,the water electrolytic cells being developed on a hypothetical plane andelectrically connected in series to one another.

[0009] With the above arrangement, an increase in electric current canbe inhibited in the water electrolytic apparatus. In addition, it ispossible to ensure that the thickness of the water electrolyticapparatus is substantially equal to the thickness of the waterelectrolytic cells, whereby the thinning of the water electrolyticapparatus can be achieved. Therefore, if the water electrolyticapparatus is superposed on a panel-shaped solar cell, the height of theentire system can be suppressed to a lower level.

[0010] The above and other objects, features and advantages of theinvention will become apparent from the following description of thepreferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a plan view of a plurality of electrolytic cells in astate in which they have been developed in a single hypothetical plane;

[0012]FIG. 2 is an enlarged sectional view of an embodiment of a waterelectrolytic apparatus, taken along a line 2-2 in FIG. 1;

[0013]FIG. 3 is an exploded perspective view of the embodiment of thewater electrolytic apparatus;

[0014]FIG. 4 is a plan view of another embodiment of a waterelectrolytic apparatus; and

[0015]FIG. 5 is an exploded perspective view of the another embodimentof the water electrolytic apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will now be described by way of embodimentswith reference to the accompanying drawings.

[0017] Referring to FIGS. 1 to 3, a water electrolytic apparatus 1includes a plurality of water electrolytic cells 2 which are developedin one hypothetical plane and electrically connected in series to oneanother.

[0018] Each of the water electrolytic cells 2 is of a rectangularparallelepiped shape as a whole and has a laminated structure. As bestshown in FIG. 2, the water electrolytic cell 2 has a solid polymerelectrolyte membrane 3 (for example, Nafion made by du Pont de Nemours.E.I., and Co.) having a proton conductivity at a central portionthereof. An current collector 5 having a seal member 4 around its outerperipheral edge and a plate-shaped anode 7 likewise having a seal member6 around its outer peripheral edge are disposed sequentially on an uppersurface of the membrane 3. On the other hand, an current collector 9having a seal member 8 around its outer peripheral edge and aplate-shaped cathode 11 likewise having a seal member 10 around itsouter peripheral edge are disposed sequentially on a lower surface ofthe membrane 3. A catalyst layer 12 containing iridium (Ir) is providedon the upper surface of the solid polymer electrolyte membrane 3 on theside of the anode 7, and a catalyst layer 13 containing platinum (Pt) isprovided on the lower surface of the solid polymer electrolyte membrane3 on the side of the cathode 11.

[0019] As best shown in FIG.1, a positive terminal 14 existing at oneend of the anode 7 protrudes to the outside from one end face of theseal member 6. In the cathode 11, a negative terminal 15 existing at theother end opposite the positive terminal 14 protrudes to the outsidefrom the other end face of the seal member 10.

[0020] The plurality of water electrolytic cells 2 are arranged, so thatlonger sides of the adjacent cells 2 are parallel to each other, and thepositive terminals 14 (and the negative terminals 15) are disposed in azigzag fashion. Thus, the anodes 7 of the water electrolytic cells 2 aredisposed on one side, an upper on hypothetical plane, and the cathodes11 are disposed on the other side, a lower hypothetical plane.

[0021] In this case, the number of water electrolytic cells 2 is an evennumber, and the positive terminal 14 of the water electrolytic cell 2located on one of the outermost sides and the negative terminal 15 ofthe water electrolytic cell 2 located on the other outermost side aredisposed on the same side and function as terminals for connection to apower supply. In the adjacent water electrolytic cells 2, at each endthereof, the upper positive terminal 14 and the corresponding lowernegative terminal 15 are connected to each other through a conductiveplate 16. Thus, the plurality of water electrolytic cells 2 areelectrically connected in series to one another.

[0022] As clearly shown in FIGS. 2 and 3, first and second flowpath-defining flat box-shaped members 17 and 18 are disposedrespectively above and below all of the water electrolytic cells 2 tosandwich these water electrolytic cells 2. The inside of the first flowpath-defining member 17 functions as a flow path 19 for water andoxygen. The first flow path-defining member 17 has a water supply port20 in one of sidewalls thereof and a water/oxygen discharge port 21 inthe other sidewall. A plurality of openings 23 are formed in a bottomwall 22 of the member 17 to face the anodes 7, respectively, and eachhave a peripheral edge put into close contact with the seal member 6 ofeach of the anodes 7 in a sealing manner. Each of the anodes 7 has aplurality of elongated communication bores 24 which permit thecommunication between each of the openings 23 and the current collector5 and thus the solid polymer electrolyte membrane 3. The communicationbores 24 serve as water outlets and inlets and as oxygen outlets. Theinside of the second flow path-defining member 18 functions as ahydrogen flow path 25 and has a hydrogen outlet 26 in one of sidewallson the side where the water/oxygen discharge port 21 exists. A pluralityof openings 28 are formed in a ceiling wall 27 to face the cathodes 11and each have a peripheral edge put into close contact with the sealmember 10 of each of the anodes 11 in a sealing manner. Each of thecathodes 11 has a plurality of communication bores 29 which permit thecommunication between each of the openings 28 and the current collector9 and thus the solid polymer electrolyte membrane 3. Each of thecommunication bores 29 is formed into an elongated shape, as are thecommunication bores 24 in the anode 7, and serves as a hydrogen outlet.Thus, the single water/oxygen flow path 19 and the single hydrogen flowpath 25 are shared by the plurality of water electrolytic cells 2. Thiscan provide the simplification of a flow path structure and anenhancement in flow path formability, as compared with a case where twotypes of independent flow paths 19 and 25 are provided in each of waterelectrolytic cells 2 so that the flow paths are connected together inseries.

[0023] A panel-shaped solar cell 30 as a power supply is superposed ontoan upper surface of the first flow path-defining member 17. A lead wire31 from a positive terminal of the solar cell 30 is connected to theoutermost positive terminal 14 of the water electrolytic apparatus 1,and a lead wire 32 from a negative terminal of the solar cell 30 isconnected to the outermost negative terminal 15 of the waterelectrolytic apparatus 1.

[0024] If the water electrolytic apparatus is constructed as describedabove, an increase in electric current can be inhibited in the waterelectrolytic apparatus 1. In addition, the thickness of the waterelectrolytic apparatus 1 can be made substantially equal to that of eachof the water electrolytic cells 2 and thus, the thinning of theapparatus 1 can be achieved. Therefore, if the water electrolyticapparatus 1 is superposed onto the panel-shaped solar cell 30, theheight of the resulting assembly can be suppressed to a lower level.

[0025] During production of hydrogen, a reaction represented byH₂O→2H⁻+½O₂+2e⁻ occurs on the side of the anode 7, and a transfer ofprotons is conducted in the solid polymer electrolyte membrane 3.Further, a reaction represented by 2H⁺+2e⁻→H₂ occurs on the side of thecathode 11.

[0026] A water electrolytic apparatus shown in FIGS. 4 and 5 includes aplurality of water electrolytic cells 2 developed all over a single flatplate 33. Each of the water electrolytic cells 2 has a first flow pathdefining member 17 including water and oxygen flow paths, and a secondflow path defining member 18 including a hydrogen flow path. The waterelectrolytic cells 2 in first and third rows arranged in a left-to-rightdirection in FIGS. 4 and 5 are placed on the flat plate 33 with thefirst flow path-defining member 17 for water and oxygen located on anupper side and with the second flow path-defining member 18 for hydrogenplaced on a lower side. On the other hand, the water electrolytic cells2 in second and fourth rows are placed on the flat plate 33 with thesecond flow path-defining member 18 for hydrogen located on an upperside and with the first flow path-defining member 17 for water andoxygen placed on a lower side. The positive terminal 14 of the waterelectrolytic cell 2 at a left end of the first row and the negativeterminal 15 of the water electrolytic cell 2 at a left end of the fourthrow are connected to the power supply. In the water electrolytic cells 2in the first and second rows, the anodes 7 and the cathodes 11 areconnected in series from the left end to the right end throughconductors 34 in an order of the first row→the second row→the firstrow→the second row --- the second row. In the water electrolytic cells 2in the third and fourth rows, the anodes 7 and the cathodes 11 areconnected in series from the right end to the left end throughconductors 35 in an order of the third row→the fourth row→the thirdrow→the fourth row --- the fourth row. Further, the cathode 11 of thewater electrolytic cell 2 at the right end of the second row and theanode 7 of the water electrolytic cell 2 at the right end of the thirdrow are connected to each other through a conductor 36. Thus, theplurality of water electrolytic cells 2 are electrically connected inseries to one another. The first flow path-defining members 17 in thewater electrolytic cells 2 at the left ends of the first to fourth rowsare connected to a water supply pipe 38 through conduits 37, and thefirst flow path-defining members 17 in the water electrolytic cells 2 atthe right ends of the first to fourth rows are connected to awater/oxygen discharge pipe 40 through conduits 39. Further, the firstflow path-defining members 17 of the adjacent water electrolytic cells 2in each of the rows are connected to each other through a conduit 41.

[0027] The second flow path-defining members 18 of the waterelectrolytic cells 2 at the right ends of the first to fourth rows areconnected to a hydrogen discharge pipe 43 through conduits 42. Further,the second flow path-defining members 18 of the adjacent waterelectrolytic cells 2 in each of the rows are connected to each otherthrough a conduit 44.

[0028] Although the embodiments of the present invention have beendescribed in detail, it will be understood that the present invention isnot limited to the above-described embodiments, and variousmodifications in design may be made without departing from the spiritand scope of the invention defined in claims.

What is claimed is:
 1. A water electrolytic apparatus comprising aplurality of water electrolytic cells each having a solid polymerelectrolyte membrane, an anode, and a cathode, the anode and the cathodebeing arranged on opposite sides of said electrolyte membrane,respectively, said water electrolytic cells being developed on ahypothetical plane and electrically connected in series to one another.2. A water electrolytic apparatus according to claim 1 , furtherincluding a solar cell serving as a power supply for said plurality ofwater electrolytic cells.
 3. A water electrolytic apparatus according toclaim 1 or 2 , wherein the anodes of the plurality of water electrolyticcells are disposed on one hypothetical plane, and the cathodes of theplurality of water electrolytic cells are disposed on anotherhypothetical plane, and a single water/oxygen flow path and a singlehydrogen flow path are shared by the plurality of water electrolyticcells.
 4. A water electrolytic apparatus according to claim 2 , whereinsaid solar cell is of a panel shape and superposed on said plurality ofwater electrolytic cells.
 5. A water electrolytic apparatus according toclaim 3 , wherein said solar cell is of a panel shape and superposed onsaid plurality of water electrolytic cells.